P826: THE CIRCULAR RNA OF THE CHAPERONIN-CONTAINING TCP1 SUBUNIT 3 GENE (CIRC-CCT3) IS OVEREXPRESSED IN MULTIPLE MYELOMA AND PREDICTS A FAVORABLE PROGNOSTIC OUTCOME, INDEPENDENTLY OF THE R-ISS STAGING
Authors: Maria Papatsirou, Christos Kontos, Ioannis Ntanasis-Stathopoulos, Panagiotis Malandrakis, Foteini Theodorakakou, Christine Liacos, Nefeli Mavrianou-Koutsoukou, Despina Fotiou, Magdalini Migkou, Maria Gavriatopoulou, Efstathios Kastritis, Meletios A. Dimopoulos, Andreas Scorilas, Evangelos Terpos
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Several non-coding RNAs, including circular RNAs (circRNAs), are associated with the onset and progression of multiple myeloma (MM). In particular, circ-CCT3 has recently been associated with MM progression and drug resistance, mostly by microRNA sponging. However, its prognostic utility in MM has not been examined, yet. Aims: Our aim was to investigate the expression levels of circ-CCT3 in MM patients’ plasma cells and compare them with those of patients with monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM), in order to examine the clinical significance of this circRNA. Moreover, we examined the potential prognostic significance of circ-CCT3 in MM. Methods: 175 bone marrow aspirate (BMA) samples were collected from adult patients with plasma cell disorders; all samples were immediately processed for CD138+ selection of plasma cells among mononuclear cells. Fluorescence in situ hybridization was used to assess the presence of high-risk cytogenetics. The ISS and revised ISS (R-ISS) staging systems were implemented for the classification of MM patients. The MM cell lines L-363, H929, and U266 were also cultured. Total RNA extraction from the samples and cell lines was followed by reverse transcription, prior to the pre-amplification of circ-CCT3 and GAPDH (reference gene). An in-house protocol was then developed for circ-CCT3 quantification by nested real-time qPCR, using divergent PCR primers. circ-CCT3 expression was measured in relative quantification units (RQU). Results: The patients’ cohort consisted of 110 newly diagnosed MM, 35 with SMM, and 30 with MGUS. The median age of all patients at diagnosis was 70 years; 106 out of the 175 cases (60.6%) were male and 69 (39.4%) were female. Moreover, 23 (20.9%) MM patients had R-ISS stage I, 62 (56.4%) had R-ISS stage II, and 25 (22.7%) had R-ISS stage III. Regarding the primary treatment of MM patients, 73 (66.4%) were treated with combinations of proteasome inhibitor (PI)-based and IMiD, 18 (16.4%) received anti-CD38–based treatment, 12 (10.9%) received PI-based therapy, and 7 (6.3%) received IMiD-based treatment. Seventy-six (69.1%) MM patients presented with osteolysis at diagnosis. The expression levels of circ-CCT3 differed between MM and SMM patients’ CD138+ plasma cells (median RQU=16.24 for MM vs. 3.07 RQU for SMM, P=0.022). On the other hand, circ-CCT3 levels did not differ significantly among the three MM cell lines. circ-CCT3 expression was not associated either with any assessed cytogenetic abnormality, the presence of osteolytic lesions, or the front-line therapy of MM patients. Regarding the overall survival (OS), MM patients with high circ-CCT3 expression had higher OS probabilities (P=0.006); this favorable prognostic significance of circ-CCT3 expression concerns progression-free survival (PFS) (P=0.015), as well. Bootstrap multivariate Cox regression analysis showed that the favorable prognostic value of circ-CCT3 is independent of R-ISS stage and age of MM patients (for OS: HR=0.24, BCa 95% CI=0.049-0.58, P=0.005; for PFS: HR=0.44, BCa 95% CI=0.21-0.79, P=0.008). Interestingly, MM patients with R-ISS II disease expressing circ-CCT3 in plasma cells had survival probabilities similar to those with R-ISS I MM, whereas R-ISS II MM patients expressing circ-CCT3 at very low levels have an OS and PFS similar to the ones of R-ISS III MM patients (Figure 1). Summary/Conclusion: circ-CCT3 is significantly upregulated in MM patients’ plasma cells, compared to SMM patients. Moreover, circ-CCT3 constitutes a favorable prognostic factor in MM, independent of ISS and R-ISS.Keywords: Smoldering, Prognosis, Multiple myeloma, Monoclonal gammopathy